GARN standby loss?

[Jim K in PA]

As for the cost subject, there's actually a lot of engineering in that fan design. It would probably have been cheaper to buy someting that was ready made. Debris can easily make it to the fan as one customer discovered when he lit his fire with newspaper. Made an awful racket when it hit the fan.

There is no doubt some loss from the open flue via natural convective air flow so closing it when the blower is off would mitigate it. The question becomes is it worth it and is it safe. What if there is no "proving circuit" in the motorized damper and it stays closed when the fan is turned on. A person wouldn't notice it until the fire was well established. A person would want to consider all the scenarios and design for worst case.

I think a 90 down into a barrel with a foot or foot and a half of pipe would definitely have an effect on the off cycle losses.

I have been burning a lot of construction and demo scrap this season leftover from the restoration of and addition to my farmhouse. I have had numerous cut nails from the 19th c. scraps make all the way to, and past, the draft inducer fan. That thing moves air very well, and I would not want to interfere with that side of things.

As you point out Steve, a "proving circuit" would be a desirable thing if/when incorporating an intake damper. A motorized damper that is power open and close, with an end switch to control the fan relay would make sure it is open before the fan starts turning. Not too hard to incorporate.

 

[foxt]

Wow, cut nails sucked that far down the path? I don't intend to burn anything but cordwood, and so far haven't noticed anything make it to the fan, not even embers out the exhaust. It's only been a couple of months, I'll have to pull that first cleanout to see what I can see ...

I already have a class A tee with a cleanout in the flue in order to vent to the side of the enclosure (ok'd by Martin), and I wonder what additional resistance the additional 90 would introduce especially projected into the barrel? The damper is easy enough to rig with some kind of failsafe to ensure it's open before the fan is enabled (an end switch such as Jim suggested), although I realize that nothing mechanical is going to be 100% bulletproof ...

Tom